The invention relates to a charged particle beam device, comprising a charged particle source for emitting a charged particle beam, a column provided with particle-optical elements which are enclosed by a column jacket and which serve to accelerate and focus the charged particle beam, the charged particle source comprising an emitter which is accommodated in an emitter chamber.
A charged particle beam device of this kind is known from: C. J. Rakels, J. C. Tiemeijer and K. W. Witteveen; "The Philips electron microscope EM 300", Philips Technical Review, Vol. 29, 1968, pp. 370-386.
The cited article describes an electron microscope in which the electron source, comprising a point-shaped emitter, accommodated in an emitter chamber, and a Wehnelt cylinder, is suspended from the column jacket by way of its side which is remote from the column. This has a drawback in that the electron source is sensitive to vibrations which are transmitted via the column jacket and which cause the electron source to move with respect to the column. A further source of interference is formed by electromagnetic fields. Despite the shielding of the electron source by the column jacket which is made of, for example, soft iron, electromagnetic fields are capable of disturbing the electron emission by the source, thus affecting the imaging. Another source of interference may be the supply leads for the high voltage of the electron source. Parasitic signals which reduce the emission stability of the source, may occur on said supply leads.
When use is made of a thermal electron source having an emitter of, for example, W or LaB.sub.6, a crossover of the electron beam has a diameter of 10-20 .mu.m. As a result, such an electron source is less sensitive to vibrations than, for example, a field emission source such as a cold field emitter or a thermal field emitter (a Schottky field emitter) having a virtual source with a diameter of a few nm. The field emission sources also require a higher vacuum than thermal electron sources, for example, 10.sup.-9 -10.sup.-10 Torr, so that additional pumping capacity is required which itself may cause additional mechanical or electromagnetic vibrations. It is inter alia an object of the invention to provide a charged particle beam device in which the charged particle source is free from mechanical and electromagnetic disturbances.